| 摘要 |
An image trap filter used in a radio frequency receiver for filtering an image signal from a radio frequency signal. The image trap filter includes an inductor and a capacitor connected in series in a first branch with the first branch connected in parallel with an impedance in a second branch. For low-side injection of the local oscillator signal (i.e., the frequency of the local oscillator signal is lower than the radio frequency signal), the impedance in the second branch is a capacitor and the series-connected inductor and capacitor in the first branch resonate at the frequency of the image signal and present a low impedance at the frequency of the image signal and a somewhat higher inductive impedance at the frequency of the radio frequency signal that resonates with the capacitor in the second branch at the frequency of the radio signal. For high-side injection of the local oscillator signal (i.e., the frequency of the local oscillator signal is higher than the frequency of the radio frequency signal), the impedance in the second branch is an inductor and the series-connected inductor and capacitor in the first branch resonate at the frequency of the image signal and present a low impedance at the frequency of the image signal and a somewhat higher capacitive impedance at the frequency of the radio frequency signal that resonates with the inductor in the second branch at the frequency of the radio signal.
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